The present invention relates generally to the use of a brine flow meter for metering brine (sodium chloride solution) to an electrolytic cell for the production of chlorine and caustic. More particularly, the present disclosure relates to an improved brine flow meter made of a plastic material advantageously resistant chemically to a wide range of pH necessary for brines of various pH levels being utilized in today's commercial chlorine and caustic cells. This employs the use of a polysulfone material, which retains the clarity necessary for visual perception of the flow of brine into the electrolytic cell, while providing substantially increased resistance to chipping and breaking due to chemical attack from brines having a high pH. Furthermore, this flow meter utilizes an additional tube around the outside of the polysulfone material to prevent ultraviolet attack of the polysulfone used for the brine meter itself.
Chlorine and caustic are essential in large volume basic commodity chemicals required by all industrialized societies. They are produced almost entirely electrolytically from aqueous solutions of alkali metal chlorides, with the major portion of such production coming from diaphragm-type electrolytic cells. In the diaphragm cell process, brine is fed continuously to the anode compartment and flows through the diaphragm usually made of asbestos, backed by a cathode. To minimize back migration of hydroxide ions, the flow rate is always maintained in excess of the conversion rate so that the resulting catholyte solution has unused alkali metal chloride present. However, to maintain the amount of unused alkali metal chloride present to an absolute minimum, it is essential to very carefully meter in the brine to the electrolytic cell by utilizing a brine flow meter or some device for such careful control. It is very important that the operator be permitted to visually perceive the amount of brine flowing into the electrolytic cell and to control such flow so as to run a constant check on the amount of unused alkali metal chloride present in the catholyte. The hydrogen ions are discharged from the solution at the cathode in the form of hydrogen gas. The catholyte solution containing caustic soda, unreacted sodium chloride and other impurities then must be concentrated and purified to obtain marketable alkali metal hydroxide commodity and alkali metal chloride, which can be reused in the chlorine and caustic electrolytic cell for further production of chlorine and caustic. Recent advances in hydraulically impermeable cation-exchange membranes have allowed the electrolytic cell to produce a much higher quality caustic product by significantly reducing the impurities present in the product and also increasing the concentration of that product. These cells also require the careful control of brine flow so as to provide the best operating conditions for the electrolytic cells.
Much research and development attention has been directed to various components of the electrolytic cell, such as the anodes, anode coatings therefor and the cation-exchange hydraulically impermeable membranes. One problem that has received very little attention, though, is the brine flow meter, which is so necessary to the successful operation of an electrolytic cell. It has been found that glass flow meters for brine metering have a fatal characteristic in that they are not resistant to solutions of high pH. Thus, the use of a glass flow meter for brine metering has caused problems in those instances where the brine is maintained at a high pH to obtain economy of use of HCl used to lower the brine pH. In fact, in most instances, the glass is very often chipped by the float utilized in such flow meters, partly because of the lack of uniformity caused by use of the glass tubes, and also because of the lack of chemical resistivity to high pH levels. This very often causes chipping and, ultimately, causes a breaking of the tube because the glass is brittle and prone to mechanical damage. Such breakage has been very detrimental in interrupting the operation of an electrolytic cell and, perhaps, even a bank of electrolytic cells, in addition to causing major spill problems when the flow of brine is interrupted to the electrolytic cell.
Thus, it would be very beneficial and advantageous to the operation of an electrolytic cell to provide a brine flow meter capable of resisting brine solutions of a high pH and additionally maintaining a higher degree of uniformity in the internal wall structure of said brine meters so as to advance this ideal characteristic of brine flow meters.